Laser-assisted thermal separation of tissue

ABSTRACT

A laser-assisted method for fully or partially separating tissue such as collagen-containing tissue is provided. In one embodiment, the method pertains to a capsolurorhexis whereby the laser-assisted method is applied to the lens capsule. A light-absorbing agent is added into or onto the tissue. A light beam with a wavelength capable of being absorbed by the light absorbing agent is then directed at the tissue to cause a thermal effect at the tissue following a predetermined closed curve with the goal to avoid irregularity or potential tears in the resulting rim of the tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/854,490 filed Apr. 1, 2013, now U.S. Pat. No. 8,562,596 issued Oct.22, 2013, which is incorporated herein by reference.

U.S. patent application Ser. No. 13/854,490 filed Apr. 1, 2013 is acontinuation of U.S. patent application Ser. No. 12/286,020 filed Sep.26, 2008, now U.S. Pat. No. 8,409,182 issued on Apr. 2, 2013, which isincorporated herein by reference.

U.S. patent application Ser. No. 12/286,020 filed Sep. 26, 2008 claimspriority from U.S. Provisional Application No. 60/995,792, filed on Sep.28, 2007, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to surgeries and procedures for removingor separating tissue. In particular, the invention relates methods anddevices for performing a capsulorhexis.

BACKGROUND OF THE INVENTION

Cataracts are a common cause for poor vision. They are the leading causeof blindness with a prevalence of over 20M worldwide. In addition, thereare at least 100M eyes with cataracts causing visual acuity of less that6/60 in meters (or 20/200 in feet). Cataract extraction is the mostcommonly performed surgical procedures in the world with estimates of 10million cases worldwide and 2 million cases being performed annually inNorth America. There are three types of cataract extraction:intracapsular, small incision cataract and phacoemulsification.

Currently, intracapsular surgery is commonly performed in the developingcountries where there are less resources. In this procedure both theopacified natural lens and the lens capsule are removed together.

In small incision cataract surgery and phacoemulsification the opacifiednatural lens is removed while leaving the elastic lens capsule intact toallow implantation and retention of the intraocular lens (IOL). One ofthe more critical surgical component is the capsulorhexis.

Capsulorhexis is the incision in the lens capsule to permit removal ofthe lens nucleus and cortex. The lens capsule is a transparent,homogeneous basement membrane that is made up of collagen-like protein.It has elastic properties without being composed of elastic fibers. Thecapsule has a smooth surface contour except at its equator where thezonules attach.

Ideally the capsulorhexis creates a symmetric circular incision,centered about the optical axis and is sized appropriately for the IOLand patient's condition. The mechanical integrity around the newlyformed incision edge needs to be sufficient to withstand the forcesexperienced during cataract extraction and IOL implantation. Bymaintaining integrity of the remaining capsule, the IOL haptics arelocated in proximity of the capsule equator to allow location of theIOL. Postoperatively the newly formed capsule rim hardens and theopening contracts providing further strengthen and structural supportfor the IOL to prevent dislocation and misalignment. Because of thispostoperative contraction it is important that the opening diameter andthe IOL optic diameter are purposefully mismatched, otherwise theresultant pressures may cause the IOL to be dislocate.

The current standard of care for capsulorhexis is Continuous CurvilinearCapsulorhexis (CCC). The concept of the CCC is to provide a smoothcontinuous circular opening through the anterior lens capsule forphacoemulsification and insertion of the intraocular tens minimizing therisk of complications including errant tears and extensions. Currently,the capsulorhexis is performed manually utilizing, forceps or a needle.The technique is dependent on applying a shear force and minimizingin-plane stretching forces to manually tear the incision.

The size of the capsulorhexis is determined by technique, the zonulesstrength and IOL optic diameter. Zonular strength is assessed prior tocapsulorhexis. If the zonules appear strong then the capsulorhexisdiameter should measure about 4-5 mm being about 0.5 to 1.0 mm smallerthan the IOL optic diameter and centered on the optical axis. Thisprovides overlap with the IOL and some margin for error. If theassessment shows a generally loose lens diaphragm then the capsulorhexisshould made about 5 to 7 mm in diameter being about 0.5 to 1.0 mm largerthan the IOL optic diameter, again centered on the optical axis. If thezonular strength assessment shows asymmetric weakness the capsulorhexisshould still be 5 to 7 mm in diameter being 0.5 to 1.0 mm larger thanthe IOL optic diameter, but located off-center away from the possibledehiscence. The would allow the IOL optic to be aligned and centered upwith the capsulorhexis when the haptics is orientated toward thequadrant of zonular weakness. Larger diameter capsulorhexis are moredifficult because the steepness of the capsule wall increases towardsthe capsule, equator, thus its harder to limit the shear forces withoutstretching the capsule, and the probability increases of a rhexisescape, i.e., an errant tear.

Errant tears are radial rips and extensions of the capsulorhexis towardsthe equator, moreover if a zonular attachment is encountered the tear issent directly out to the capsular fornix and possibly through to theposterior of the capsule. Furthermore, posterior capsule tearsfacilitate the nucleus being “dropped” into the posterior chamberresulting in further complications.

Further problems that may develop in capsulorhexis are related toinability of the surgeon to adequately visualize the capsule due to lackof red reflex, to grasp it with sufficient security, to tear a smoothsymmetric circular opening of the appropriate size or technicaldifficulties related to maintenance of the anterior chamber depth afterinitial opening, small size of the pupil, or the absence of a red reflexdue to the lens opacity. Additional complications arise in olderpatients with weak zonules and very young children that have very softand elastic capsules, which are very difficult to mechanically rupture.

Errant tears and other problems can be managed to some degree with theaddition of dense viscoelastics and relaxing incisions to assist instabilization of the capsule rim. If need be a two-stage capsulorhexistechnique can be required to rescue a situation or for the formation ofa second large capsulorhexis. Specifically, after creating an initialcapsulorhexis, the anterior cortex is removed with aspiration andirrigation and capsule is refilled with viscoelastic to stabilize thecapsule and the capsulorhexis is enlarged by tearing larger secondcapsulorhexis.

Further stress is applied to the capsulorhexis in phacoemulsificationand implantation of the IOL, if the capsulorhexis is discontinuous or ifthe force is too great the capsulorhexis may cause a radial tear. Thisis dealt with as above. Furthermore if the posterior capsule integrityis damaged during the cataract surgery (i.e., a posterior capsule rent)dense viscoelastic is added to preserve its shape and a posteriorcapsulorhexis is performed, to salvage the integrity and strength of thecapsule around its equator such that an IOL can be implanted.

Most current cataract surgeries are performed with the aid ofphacoemulsification and typically includes the following eighteen steps.

-   -   1. Pupil Dilation    -   2. Local Anesthesia    -   3. Placement of the lid speculum    -   4. Entry into the eye through a small incision (typically 2-3 mm        in length, at the edge of the cornea)    -   5. Viscoelastic injected into the anterior chamber and to        maintain the volume and shape of the Anterior chamber and cornea        during the rest of the procedure    -   6. Zonule function test    -   7. Capsulorhexis    -   8. Hydrodissection are intended to identify and soften tyre        nucleus for the purposes of removal from the eye.    -   9. Hydro-delineation increases the distance between the nucleus        and the posterior capsule, thus providing a safety zone.    -   10. Nuclear cracking or chopping if needed    -   11. Ultrasonic with aspiration and irrigation are used to sculpt        and emulsification of the nucleus used to sculpt the relatively        hard nucleus of the lens.    -   12. Aspiration of the residual soft cortex    -   13. Capsular polishing    -   14. once the capsule is empty further addition of viscoelastic        to maintain the volume and shape of the capsule    -   15. Implantation of the artificial IOL    -   16. Centration of the    -   17. Viscoelastic removal    -   18. Wound sealing/hydration (if needed)

Following cataract surgery there is a rapid 1-2 days response where thecapsule hardens and the capsule contraction starts. This continues overa 4-6 week period where fibrosis of the capsulorhexis and opticinterface, and the haptic and capsule interfaces also occur. Even beyondone year the capsule continues to contract to a lesser degree, thuspositioning the capsulorhexis is a critical factor in the long-termsuccess.

Following cataract surgery one of the principal sources of visualmorbidity is the slow development of opacities in the posterior lenscapsule, which is generally left intact during cataract surgery as amethod of support for the lens, and also as a means of preventingsubluxation posteriorly into the vitreous cavity. It has been estimatedthat the complication of posterior lens capsule opacification occurswithin 5 years of surgery with a 10% incidence. This problem is thoughtto occur as a result of epithelial and fibrous metaplasia along theposterior lens capsule centrally from small islands of residualepithelial cells left in place near the capsule equator. The Q-switchNd:YAG lasers are utilized as to perform a noninvasive posteriorcapsulotomy to remove the opacification from the proximity of theoptical axis.

Accordingly, there is a need in the art to provide new ophthalmicmethods, techniques and apparatus to advance the standard of care forcapsulorhexis

SUMMARY OF THE INVENTION

The present invention provides a laser-assisted method for separatingtissue such as collagen-containing tissue. In one embodiment, the methodis a capsolurorhexis whereby the laser-assisted method is applied to thelens capsule.

A light-absorbing agent is added into or onto the tissue. A light beamwith a wavelength capable of being absorbed by the light absorbing agentis then directed at the tissue to cause a thermal effect at the tissue.The light beam is: (i) characterized to remain at a sub-ablation levelof the tissue or (ii) characterized to cause melting of the tissue. Thelight beam could either cause a full or partial separation, cutting orpuncture of the tissue.

A predetermined closed curve is defined at the tissue. This curvedefines an interior and an exterior. The light beam is directed at aninitial and interior point of the predetermined closed curve. Once aninitial puncture or partial/full separation has been achieved, the lightbeam continues and is further directed starting from the initial andinterior point of the predetermined closed curve along the remainingpath of the predetermined closed curve until at least the curve isclosed. In one embodiment, the continued light beam ends at a final andinterior point of the predetermined closed curve.

The initial and the continuing light beam(s) could be the same type oflight beam or different types of light beams. In a preferred embodiment,the light beam is a laser beam from a CW laser. A CW laser is preferredfor at least the continuing light beam to allow for a single pass alongthe curve to avoid irregularity or potential tears in the resulting rimof the tissue. The exterior path of the predetermined closed curve ispreferably substantially circular or ellipsoidal in the application of acapsulorhexis but is not limited to these shapes in other applications.

Visualization patterns could be added and projected at the tissue whichwill aid in the procedure. The visualization patterns useful in thisinvention (i) are different from the predetermined closed curve or (ii)include of at least 3 set of dots, wherein each of the set of dots isdistributed along the interior-exterior border of the predeterminedclosed curve.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with its objectives and advantages willbe understood by reading the following description in conjunction withthe drawings, in which:

FIG. 1 shows according to an embodiment of the present invention atranverse plane view of some parts of the eye (lens capsule 110, IOL120, dialated iris 140, cornea 160 and anterior chamber 170), a lightabsorbing agent 130 and a light beam 150.

FIG. 2 shows according to an embodiment of the present invention a sideview of the lens capsule 110 whereby the tissue (in this example lenscapsule 110) has been separated at 210 into two parts, e.g. an exteriorpart 110-E and an interior part 110-I. FIG. 2 also shows the contractedand shrinked ends 220-E and 220-I.

FIG. 3 shows according to an embodiment of the present invention acoronal plane view from an anterior direction of a tissue (in thisexample lens capsule 110) with a predetermined closed curve 310. It isimportant to note that the predetermined closed curve starts with aninitial point inside of the closed curve. In one embodiment, thepredetermined closed curve ends at any point where the curve becomesclosed. In another embodiment, the predetermined curve end withend-point within the interior area.

FIGS. 4A-B show according to an embodiment of the present invention avisualization pattern 410, which preferably coincides with the perimeterof the closed curve (e.g. a circular pattern in this particularexample). It is important to note that the visualization pattern 410does not include the initial and end paths inside the interior area.FIGS. 4A-B also show another visualization pattern with at least 3 setof dots 420 to assist in focusing the light beam(s), whereby the set ofdots preferably are visualized along the interior-exterior border of theclosed curve 310. FIG. 4A shows 4 sets of dots and FIG. 4B shows 3 setsof dots. Visualization pattern 410 and 420 could be used separately ortogether.

DETAILED DESCRIPTION

FIG. 1 shows a transverse plane view of part of the eye. For thepurposes of this invention the lens capsule 110 and the IOL 120 areshown including the iris 140 in dialated position. The anterior lenscapsule is transparent and therefore does not readily absorb light.Prior attempts to use a laser to remove tissue or make a capsulorhexisin the lens capsule have utilized (i) photodisruption producingcavitation and/or mechanical shockwave, e.g. the Q-switch Nd:YAG lasersused for posterior capsulotomy, or (ii) plasma induced ablation e.g.,the sub-pico second laser for 3-D scanned Capsulorhexis and nucleusfragmentation.

In this invention, a light absorbing agent 130 is added into or onto alayer of the anterior lens capsule 110. This agent could be abiocompatible agent (e.g. indocyanine green (ICG) or methyl blue), adye, pigment, a nanoparticle, a carbon particle, or a like.Subsequently, a light beam 150, e.g. a laser, is directed to theanterior lens capsule. The directed light beam is absorbed by the lightabsorbing agent with the intent to cause a local thermal affect on theanterior lens capsule that yields a capsulorhexis. In other words, thewavelength, power, speed of light beam movement etc. of the lightbeam(s), should be selected so that it can be absorbed by the lightabsorbing agent to cause sufficient thermal energy adjacent or at theanterior lens capsule. Furthermore, the absorption of energy should besufficient to cause a mechanical separation 210 effect at the anteriorlens capsule (FIG. 2). In general, the light beam(s) are set to be at asub-ablation level of the anterior lens capsule or are set to causelocal melting or partial/full separation of the anterior lens capsule.

The lens capsule membrane contains collagen fibrilis. As collagen isheated, it denatures, i.e. the triple-helix of collagen unwinds due tothe disruption of hydrogen bonds between the adjacent al has chains.Furthermore, collagen undergoes a transition from its crystallinehelical structure to an amorphous structure and collagenshrinkage/contraction occurs (220-E, 220-I in FIG. 2). With theapplication of controlled heat by the directed light beam to theanterior lens capsule in the temperature range between 50 degreesCelsius and 150 degrees Celsius vaporization, membrane melting andshrinkage can occur. In another embodiment, the temperature range couldbe between 100 degrees Celsius and 120 degrees Celsius.

The capsulorhexis will be formed and the immediately adjacent tissuethat forms the resultant rim will have the contracted amorphouscollagen. This resulting rim is more elastic and resistant to tearingthan the original membrane because it comprises of this amorphouscollagen and no additional mechanical forces have stress/fractured therim during this process. The shrieked and contracted ends 220E and 220-Iseparate (see 210) as a result of the directed light the anterior lenscapsule 110 into the part that remains in the eye 110-E and the partthat eventually is removed 110-I for the purposes of a capsulorhexis.

One of the key aspect of the invention is the pattern of the light beamdirected at the anterior lens capsule (FIG. 3). FIG. 3 is a coronalplane view from an anterior direction of the lens capsule 110. Apredetermined closed curve 310 is defined that will be used to directthe light beam(s) and perform the capsulorhexis. The closed curve 310defines an interior and exterior area, whereby the interior area isenclosed by the closed curved 310 as shown in FIG. 3. The exterior areais anything outside the circumference of the closed curve 310. Thepredetermined closed curve distinguished an initial starting point(initial) located in the interior area. Optionally the predeterminedclosed curve also include an ending point (end) located in the interiorarea. The predetermined closed curve can be (pre)-programmed and addedto the laser and optical system used for the performance of thecapsulorhexis.

During execution, a light beam is directed to the initial point on theclosed curve 310. The selection of the position of the initial point isto create an initial starting hole, puncture or separation in theanterior lens capsule while staying clear from the ultimate position ofthe rim of curve 310 upon capsulotomy. Since the initial point is insidethe closed curve it avoids irregularity or potential tears in theresulting rim of the remaining anterior lens capsule (i.e. 220-E).

Once the initial point is created by the light beam and according to oneembodiment, the light beam is directed from the initial point of thepredetermined closed curve and continues (in the direction of the errorand in this example counterclockwise) along the pattern of thepredetermined closed curve until at least the curve is closed. In oneembodiment, this endpoint could be at end as shown in FIG. 3 i.e. at theinterior part of the closed curve again to avoid irregularity orpotential tears in the resulting rim of the remaining anterior lenscapsule or in another embodiment at any point once the curve is closedat the border of the interior/exterior area. For the purposes of acapsulorhexis, the shape of the exterior perimeter of the closed curveis preferably substantially circular or ellipsoidal.

The light beam at the initial point or the continued light beam alongthe curve path could be the same light beam or could be different lightbeams either with the same of different characteristics or parameters.The initial point could also be seen as an initial puncture beforefollowing the path of the curve and, according to this example, theinitial light beam could then be different from the continuing lightbeam.

In one embodiment, for example, but not limiting to the scope of theinvention, the initial light beam or puncture could have the followingparameters:

-   -   Speed of movement: 0 to 10 mm/second, basically dwelling on one        location or oscillating a small region for a time of about 0.25        to 3 sec.    -   Diameter of light beam on the surface: 50-600 microns.    -   Power of light beam dependent on the light absorbing agent, but        ideally less than 1000 mW.

In one embodiment, for example, but not limiting to the scope of theinvention, the continuing light beam which at least closes the curvecould have the Mowing parameters:

-   -   Speed of movement: 0.25 to 10 mm/second, preferably in a single        pass along the curve.    -   Diameter of light beam on the surface: 50-600 microns.    -   Power of light beam dependent on the light absorbing agent, but        ideally less than 1000 mW.

In a preferred, embodiment, for example, but not to the scope of theinvention, the continuing light beam which at least closes the curvecould have the following parameters:

-   -   Speed of movement: 0.5 to 3 mm/second, preferably in a single        pass along the curve.    -   Diameter of light beam on the surface: 100-300 microns.    -   Power of light beam dependent on the light absorbing agent, but        ideally less than 600 mW.

The continuing light beam is preferably accomplished in a single pass toprovide as much consistency in the rim pattern as possible with the rimbeing formed with the same (or at least similar) thermal conditions. Thesingle pass is also important to ensure completion of the capsulorhexiseven if there is slight movement of the eye relative to the trajectory.Preferably and in particular for the continuing light beam a CW laser isused. However, a high-frequency pulsed (>1 KHz) pulsed laser, e.g. asubpico Q-switch laser could also be used. In one embodiment, thewavelength could be in the infrared to near infrared region of thespectrum, thus it would be near invisible to the patient, providingminimal irritation.

A visible aim beam or pattern(s) could be present to project thelaser-cutting or laser-separating trajectory or to project at least partof the closed curve on the anterior lens capsule surface. Thevisualization patterns are useful to bring the laser into focus on thelens capsule surface and to allow the physician to select the locationand size of the capsulorhexis. To get the visible aim beam into focus isoften hard, especially for a ring, since you are looking for a sharpedge on the aim beam or its smallest width of the line.

To assist focusing the method described herein could be extended byprojecting a visualization pattern 410, which preferably coincides withthe perimeter of the closed curve (e.g. a circular pattern in thisparticular example) (FIG. 4). In other words, a key aspect of thisinvention is that visualization pattern 410 is different from thepattern of the closed curve 310 (i.e. 410 does not include the initialand end paths in the interior side of the closed curve). FIG. 4 alsoshow another visualization pattern with at least 3 set of dots 420 toassist in focusing the light beam(s), whereby the set of dots preferablyare visualized along the interior-exterior border of the closed curve310. Such a pattern of discrete dots 420 is far easier to focus and ororientating the eye of the patient. Pattern 410 and 420 could be usedseparately or combined.

In one embodiment, for example, but not limiting to the scope of theinvention, the visualization light beam could have the followingparameters:

-   -   Speed of movement: greater than 450 mm/second.    -   Diameter of light beam on the surface: 50-600 microns    -   Power of light beam is dependent on the light absorbing agent,        with an average power of less 1 mW.    -   Wavelength is in the visible spectrum.

As one of ordinary skill in the art will appreciate, various changes,substitutions, and alterations could be made or otherwise implementedwithout departing from the principles of the present invention. Forexample, in one variation the methods described herein could be variedfrom the application of a capsolurorhexis to thermally cutting orpartially/fully separating tissue or collagen-containing material. Inyet another variation, the laser-assisted capsulorhexis does notpenetrate the full thickness of the anterior lens capsule, but there isa groove in the capsule surface. The full thickness capsulorhexis couldthen be completed manually with a CCC with the groove guiding the manualtear. In still another variation, additional methods for fixating theeye could be added for example by placing a surgical contact lens on theeye. This will minimize the eye motion. Moreover, the scanning devicecould or any other device could hold the contact lens thus restrictingthe eye motion further. The use of a contact lens could also increasethe ability to focus the light with a great numerical aperture, allowingmore accurate focusing on the specific target tissue and reduction oreliminate potential light beam exposure to the retina, cornea, foveaposterior capsule and cataractus lens and therewith less of adisturbance/irritation to the patient. Accordingly, the scope of theinvention should be determined by the following claims and their legalequivalents.

What is claimed is:
 1. A device for thermally separating tissue in theanterior lens capsule of an eye in a procedure creating an opening inthe anterior lens capsule, the device comprising: a laser deviceprogrammed to direct a laser beam along a predetermined closed curve onthe anterior lens capsule; wherein the laser beam power, wavelength, anddiameter at the anterior lens capsule are selected such that the laserbeam is absorbed by a light absorbing agent in or on the anterior lenstissue to locally heat the anterior lens tissue along the closed curveand thermally transition collagen in the anterior lens capsule tissuefrom a helical structure to an amorphous structure resulting inshrinkage or contraction of the tissue along the closed curve withoutablation of the anterior lens capsule tissue, thereby separating theanterior lens capsule tissue along the closed curve to form an area ofanterior lens capsule tissue inside the closed curve and an area ofanterior lens capsule tissue outside the closed curve, the lens capsuletissue outside the closed curve defining the boundary of the opening inthe anterior lens capsule; wherein the laser device is programmed todirect the laser beam in a single pass starting at an initial pointinterior to the closed curve, then along the closed curve, and then to afinal point interior to the closed curve; wherein the laser beamdiameter at the anterior lens capsule tissue is 50 microns to 600microns; wherein the laser beam power is less than or equal to 1000 mW;wherein the laser beam is directed along the closed curve at less thanor equal to 10 millimeters/second; and wherein absorption of the laserbeam by the light absorbing agent causes a temperature increase at theanterior lens capsule along the closed curve of between 50 degreesCelsius and 150 degrees Celsius.
 2. The device of claim 1, wherein thelight absorbing agent is added to the anterior lens capsule tissue. 3.The device of claim 1, wherein the laser beam is a continuous wave laserbeam.
 4. The device of claim 1, wherein the closed curve is circular orelliptical.
 5. The device of claim 1, wherein the laser beam diameter atthe anterior lens capsule tissue is 100 microns to 300 microns.
 6. Thedevice of claim 1, wherein absorption of the laser beam by the lightabsorbing agent causes a temperature increase at the anterior lenscapsule along the closed curve of between 100 degrees Celsius and 120degrees Celsius.
 7. The device of claim 1, comprising a laser deviceprogrammed to direct a visible laser beam along a visualization patternon the anterior lens capsule to assist a user in selecting the locationand size of the opening to be created in the anterior lens capsule. 8.The device of claim 1, in combination with a surgical contact lens thatincreases the numerical aperture with which the laser beam is focusableonto the anterior lens capsule thereby reducing exposure of the retinaand the fovea of the eye to the laser beam.
 9. The device of claim 1,wherein: the laser beam is a continuous wave laser beam; and the laserbeam diameter at the anterior lens capsule tissue is 100 microns to 300microns.
 10. The device of claim 9, comprising a laser device programmedto direct a visible laser beam along a visualization pattern on theanterior lens capsule to assist a user in selecting the location andsize of the opening to be created in the anterior lens capsule.
 11. Thedevice of claim 9, wherein the light absorbing agent is added to theanterior lens capsule tissue.
 12. The device of claim 9, in combinationwith a surgical contact lens that increases the numerical aperture withwhich the laser beam is focusable onto the anterior lens capsule therebyreducing exposure of the retina and the fovea of the eye to the laserbeam.